You can use software encoding. You would select "None" from the hardware acceleration drop down. Whether your old CPU is up to the task is another story.
Jellyfin 12.0 (Docker)
Debian 13 w/Xanmod amd64v3 LTS kernel
AMD Ryzen 5500 w/32GB DDR4
Intel Arc A380
OS drive - SK Hynix P41 1TB
ZFS Storage pool
vdev1 - 6x WD Red Pro 6TB CMR in RAIDZ1
vdev2 - 3x WD Red Pro 18TB CMR in RAIDZ1